Dr. John S. Roberts Profile

Dr. John S. Roberts

at Univ of Sheffield

SPIE Involvement:

Author

Publications (20)

Proceedings Article | 26 February 2010 Paper

Higher limiting efficiencies for nanostructured solar cells

Jessica G. Adams, Warren Elder, Geoff Hill, John Roberts, Keith W. Barnham, Nicholas Ekins-Daukes

Proceedings Volume 7597, 759705 (2010) https://doi.org/10.1117/12.844114

KEYWORDS: Quantum wells, Solar cells, Quantum efficiency, Absorption, Gallium arsenide, Semiconductors, Indium, Reflectivity, Nanostructuring, Mirrors

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Proceedings Article | 12 February 2010 Paper

A platform for GaAs opto-electronic integrated circuits based on GaAs/AlGaAs regrowth upon patterned InGaP

Kristian Groom, Benjamin Stevens, Punima Greenwood, David Childs, John Roberts, Matthew Lomas, Maxime Hugues, Hifsa Shahid, Richard Hogg

Proceedings Volume 7616, 76160A (2010) https://doi.org/10.1117/12.841612

KEYWORDS: Gallium arsenide, Indium gallium phosphide, Reflectivity, Waveguides, Photonic integrated circuits, Cladding, Semiconductor lasers, Integrated circuits, Etching

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Proceedings Article | 25 October 2006 Paper

Probing the electronic and optical properties of quantum cascade lasers under operating conditions

D. Revin, M. Soulby, J. Cockburn, A. Krysa, J. Roberts, R. Airey, R. Nelander, M. Pereira, A. Wacker

Proceedings Volume 6386, 63860H (2006) https://doi.org/10.1117/12.692334

KEYWORDS: Quantum cascade lasers, Absorption, Waveguides, Electrons, Laser damage threshold, Transmittance, Polarization, Temperature metrology, Spectroscopy, Continuous wave operation

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Proceedings Article | 18 November 2005 Paper

Single mode quantum cascade lasers

M. Austerer, C. Pflügl, S. Golka, S. Schartner, W. Schrenk, R. Green, L. Wilson, J. Cockburn, A. Krysa, J. Roberts, G. Strasser

Proceedings Volume 6010, 601002 (2005) https://doi.org/10.1117/12.630501

KEYWORDS: Quantum cascade lasers, Waveguides, Gallium arsenide, Pulsed laser operation, Silicon, Continuous wave operation, Temperature metrology, Semiconductor lasers, Etching, Cladding

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Proceedings Article | 13 April 2005 Paper

Temperature dependence of the threshold electric field in a hot electron VCSEL

Ali Serpenguzel, Naci Balkan, Ayse Erol, M. Cetin Arikan, John Roberts

Proceedings Volume 5725, (2005) https://doi.org/10.1117/12.591107

KEYWORDS: Gallium, Aluminum, Vertical cavity surface emitting lasers, Temperature metrology, Reflectivity, Electroluminescence, Gallium arsenide, Quantum wells, Physics, Electronics

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Proceedings Article | 22 October 2004 Paper

High-performance quantum cascade lasers grown by metal-organic vapor phase epitaxy

Luke Wilson, Richard Green, Andrey Krysa, John Roberts, Wing Ng, Dmitry Revin, Christian Pflugl, Werner Schrenk, Gottfried Strasser, John Cockburn

Proceedings Volume 5564, (2004) https://doi.org/10.1117/12.558991

KEYWORDS: Quantum cascade lasers, Temperature metrology, Semiconducting wafers, Superlattices, Silicon, Indium gallium arsenide, Doping, Vapor phase epitaxy, Waveguides, Switching

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Proceedings Article | 18 October 2004 Paper

Optoelectronic integrated tweezers

Simon McGreehin, Liam O'Faolin, John Roberts, Thomas Krauss, Kishan Dholakia

Proceedings Volume 5514, (2004) https://doi.org/10.1117/12.559442

KEYWORDS: Particles, Optical spheres, Optical tweezers, Polymers, Optoelectronics, Etching, Optical alignment, Optical trapping, Optical manipulation, Semiconductor lasers

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Proceedings Article | 11 June 2003 Paper

Influence of temperature and free carries on four-wave mixing in semiconductor microcavities

M. Makhonin, D. Krizhanovskii, A. Dremin, A. Tartakovskii, V. Kulakovskii, N. Gippius, Maurice Skolnick, John Roberts

Proceedings Volume 5023, (2003) https://doi.org/10.1117/12.511762

KEYWORDS: Polaritons, Scattering, Excitons, Four wave mixing, Absorption, Semiconductors, Phonons, Temperature metrology, Optical microcavities, Sapphire lasers

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In semiconductor microcavities (MCs) with embedded quantum wells (QW) a strong two-dimensional (2D) confinement of the light in the growth direction leads to an enhanced exciton-photon interaction, which results in the formation of mixed exciton-photon states described in terms of quasi 2D-polaritons. The density of these states is strongly reduced compared to exciton one, due to a very small in-plane mass. As a result, one can hope that the high filling of the polariton states near the polariton band bottom can be achieved at relatively small total density without destroying the strong coupling regime. However such a filling never was reached at low excitation density range where the polariton relaxation to the polariton branch bottom is determined by the emission of acoustic phonons. The reason is in the fact that the polariton lifetime is comparable with phonon scattering time. As a result, the energy distribution of polaritons clearly demonstrates 'bottleneck effect' both under the above band gap excitation and the resonant excitation below free exciton level. However the high occupation of polariton states near the band bottom is relatively easy reached under conditions of a strong resonant excitation into the lower polariton (LP) branch at particular wavenumbers close to the inflection point of the LP dispersion. It is explained as the result of stimulated hyper-Raman scattering (or four-wave mixing) of pumped polaritons with (E_p, k_p) to states with the energy and momentum [E₁, k₁ approximately 0] and [E₂ = 2E_p - E₁, k₂ = 2k_p], which referred to as the 'signal' and 'idler,' respectively. Here we investigate the influence of a temperature and an additional above band gap excitation on the stimulated scattering in MCs. A GaAs/AlAs MC containing 6 InGaAs quantum wells in the active layer (Rabi splitting Ω of 6 - 7 meV) has been investigated in a wide range of detunings between free exciton level and bottom of the photonic mode from δ = 0 to -3 meV. The resonance excitation into an LP branch was carried out with a tunable Ti-sapphire laser. The HeNe laser was used for the additional above GaAs band gap excitation. The sample was mounted in a helium thermostat with the temperature control at T = 5 - 30 K.

Proceedings Article | 9 July 2001 Paper

Nonlinear dynamics in a graded quantum well placed in a GaAlAs p-n junction

Naci Balkan, Huseyin Sari, Andreas Schroeder, Yuksel Ergun, Ismail Sokmen, John Roberts

Proceedings Volume 4283, (2001) https://doi.org/10.1117/12.432622

KEYWORDS: Quantum wells, Electroluminescence, Gallium arsenide, Absorption, Lanthanum, Sensors, Optical fibers, Wavelength division multiplexing, Electrons, Physics

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Proceedings Article | 18 April 2000 Paper

Residual oxygen contamination of InAlGaAs SQW high-power laser diodes

John Roberts, Lesley Smith, Peter Tihanyi

Proceedings Volume 3947, (2000) https://doi.org/10.1117/12.382107

KEYWORDS: Oxygen, Indium, Quantum wells, Aluminum, Contamination, High power lasers, Semiconducting wafers, Diodes, Gallium, Cladding

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Proceedings Article | 6 August 1999 Paper

Hot-electron VCSEL

Naci Balkan, Ismail Sokmen, Angela O'Brien-Davies, Richard Potter, Carl Hepburn, Adrian Boland-Thoms, Michael Adams, John Roberts

Proceedings Volume 3625, (1999) https://doi.org/10.1117/12.356892

KEYWORDS: Vertical cavity surface emitting lasers, Quantum wells, Gallium arsenide, Reflectivity, Electroluminescence, Physics, Semiconducting wafers, Measurement devices, Electron transport, Semiconductors

Proceedings Article | 7 July 1998 Paper

Operation of a novel hot-electron vertical-cavity surface-emitting laser

Naci Balkan, Angela O'Brien-Davies, A. Thoms, Richard Potter, Nigel Poolton, Michael Adams, J. Masum, Alpan Bek, Ali Serpenguzel, Atilla Aydinli, John Roberts

Proceedings Volume 3283, (1998) https://doi.org/10.1117/12.316680

KEYWORDS: Reflectivity, Vertical cavity surface emitting lasers, Quantum wells, Electroluminescence, Gallium arsenide, Semiconductors, Electron transport, Diffusion, Lasers, Physics

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Proceedings Article | 7 July 1998 Paper

Theoretical and experimental analysis of the spontaneous emission and threshold current of edge-emitting Bragg microcavity laser structures

Graham Berry, Gareth Lewis, Huw Summers, Peter Blood, John Roberts

Proceedings Volume 3283, (1998) https://doi.org/10.1117/12.316687

KEYWORDS: Optical microcavities, Quantum wells, Mirrors, Reflectivity, Refractive index, Gallium arsenide, Polarization, Laser damage threshold, Transition metals, Waveguides

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SPIE Journal Paper | 1 April 1998

Photonic microstructures as laser mirrors

Thomas Krauss, Oskar Painter, Axel Scherer, John Roberts, Richard De La Rue

OE, Vol. 37, Issue 04, (April 1998) https://doi.org/10.1117/12.10.1117/1.601948

KEYWORDS: Mirrors, Reflectivity, Photonic microstructures, Laser damage threshold, Waveguides, Semiconductor lasers, Etching, Quantum efficiency, Photonic crystals, Electrical engineering

Proceedings Article | 2 May 1997 Paper

AlxGayIn1-x-yAs/AlGaAs quantum well lasers at 670 to 750 nm

Peter Smowton, Peter Blood, Paul Mogensen, John Roberts

Proceedings Volume 3001, (1997) https://doi.org/10.1117/12.273783

KEYWORDS: Quantum wells, Cladding, Temperature metrology, Aluminum, Indium gallium phosphide, Waveguides, Gallium, Indium, Laser damage threshold, Refractive index

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Proceedings Article | 1 May 1997 Paper

VCSELs for 640- to 1100-nm emission

Terry Sale, John Roberts, John David, R. Grey, Peter Robson

Proceedings Volume 3004, (1997) https://doi.org/10.1117/12.273833

KEYWORDS: Vertical cavity surface emitting lasers, Quantum wells, Metalorganic chemical vapor deposition, Gallium arsenide, Mirrors, Resistance, Aluminum, Silicon, Reflectivity, Reflectors

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Proceedings Article | 4 April 1997 Paper

Temperature effects in VCSELs

Terry Sale, John Roberts, John David, R. Grey, Jon Woodhead, Peter Robson

Proceedings Volume 3003, (1997) https://doi.org/10.1117/12.271056

KEYWORDS: Vertical cavity surface emitting lasers, Quantum wells, Mirrors, Instrument modeling, Reflectivity, Thermal modeling, Resistance, Data modeling, Thermal effects, Oxides

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Proceedings Article | 19 April 1996 Paper

Tuning of the exciton-photon coupling in semiconductor quantum microcavities by external electric and magnetic fields

T. Fisher, Maurice Skolnick, A. Afshar, D. Whittaker, P. Kinsler, John Roberts, Geoff Hill, M. Pate

Proceedings Volume 2694, (1996) https://doi.org/10.1117/12.238386

KEYWORDS: Excitons, Polaritons, Magnetism, Oscillators, Photons, Quantum wells, Reflectivity, Semiconductors, Optical microcavities, Solids

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Proceedings Article | 3 September 1992 Paper

Microresonator modulators: design, fabrication, and fine tuning the performance

Gareth Parry, Marco Ghisoni, P. Zouganeli, R. Mottahedeh, A. Rivers, M. Pate, Geoff Hill, John Roberts, Chris Button

Proceedings Volume 1675, (1992) https://doi.org/10.1117/12.137637

KEYWORDS: Quantum wells, Modulators, Reflectivity, Microresonators, Absorption, Fabry–Perot interferometers, Interfaces, Aluminum, Semiconducting wafers, Reflectors

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